The invention relates to a drive system for an engine arrangement, an engine arrangement including such a drive system, a vehicle comprises such an engine arrangement, and a method for operating such an engine arrangement.
The invention can be applied in medium and heavy-duty vehicles, such as trucks, buses and construction equipment.
In order to decrease fuel consumption, engine arrangements have been developed that automatically stop an engine when the engine power is not needed—for example at a traffic light or in a traffic jam, when the driver depresses the brake pedal—and restarts the engine in response to a signal—typically when the driver actuates the accelerator pedal.
Such an engine arrangement comprises the engine, an electric machine, one or several accessories, and an accessory pulley to which the electric machine and the accessory(ies) are drivingly connected. A drive system comprising a gear reduction mechanism is used to join the accessory pulley and an engine crankshaft.
The engine arrangement can be in one of:
a starting phase, in which the electric machine, powered by a battery, starts the engine;
a running phase (i.e. normal driving conditions), in which the engine is running, drives the accessory, and drives the electric machine so that said electric machine can charge the battery;
and an electric phase, in which the engine is stopped and the electric machine drives the accessory.
The drive system is designed to allow the engine arrangement to be operated in any of these three phases, and to allow for transition between these three phases.
Although conventional drive systems are generally satisfactory, room for improvement remains.
It is desirable to provide an improved drive system for an engine arrangement.
More specifically, it is desirable to provide such a drive system which allows smoother transition between at least two operating phases of the engine.
According to a first aspect, the invention relates to a drive system for an engine arrangement, the drive system comprising a gear reduction mechanism having at least three separate and rotatable junction elements, the rotation speeds of the junction elements being interdependent but not having a fixed ratio the ones relative to the others, and wherein, in the mounted position, among said junction elements:
a first junction element is connected to an engine crankshaft;
a second junction element is connected to an accessory pulley which is drivingly connected to an electric machine and at least one accessory;
a third junction element.
The drive system according to an aspect the invention further comprises a free wheel which is connected to a non-rotating part of the engine arrangement in the mounted position, the third junction element being configured to be coupled to the free wheel in a first operating phase of the drive system. In the first operating phase, the free wheel is configured such that when the third junction element exerts torque on the free wheel in one direction, the free wheel is in an engaged state and stops the rotation of the third junction element, and when the third junction element exerts torque on the free wheel in the opposite direction, the free wheel is in a free state and allows rotation of the third junction element.
In other words, the gear reduction mechanism is designed such that when the first junction element is receiving torque from the second junction element in the first operating phase, the third junction element exerts torque on the free wheel in one direction, the free wheel then being in an engaged state, and such that when the first junction element is generating a positive torque, the third junction element exerts torque on the free wheel in the opposite direction, the free wheel then being in a free state.
The mounted position means the position in which the drive system is installed within the engine arrangement and can be operated.
The “free state” of the free wheel corresponds to the configuration in which the free wheel disengages a drive member, that is connected to the free wheel or that is part of the free wheel, from a driven member, that is connected to the free wheel or that is part of the free wheel, while in the “engaged state” of the free wheel the drive member is engaged with the driven member by means of the free wheel, acting as a transmitting device. The drive member can be a driveshaft connected to the free wheel or a driveshaft of the free wheel and the driven member can be a driven shaft connected to the free wheel or a driven shaft of the free wheel.
In practice, the first operating phase corresponds to a starting phase of the engine, in which the electric machine rotates the engine up to start speed. In this starting phase, the free wheel provides a single way connection from the electric machine to the engine. Indeed:
At the beginning of the starting phase, the rotational speed of the engine is fairly low. Combustion is not established and engine needs torque to rotate. The free wheel, which receives through the third junction element a first torque oriented in one direction, is in an engaged state. This configuration allows transmission of torque from the electric machine to the engine;
When combustion is established, the engine accelerates sharply and the crankshaft provides torque. The free wheel, which receives through the third junction element a second torque oriented in an opposite direction, is in a free state and allows a free acceleration of the crankshaft. No torque, or only an insignificant torque, is transmitted from the engine to the electric machine or to the accessory. The electric machine speed is considered as being uncorrelated to crankshaft speed.
At the beginning of the starting phase, the reduction ratio between the rotational speeds of the engine and the electric machine is Ra=R0×R1a, wherein:
R0 is the reduction ratio between the electric machine and the accessory pulley. R0 can be around 4 for example;
R1a is the reduction ratio between the accessory pulley and the crankshaft. R1a can be around 4 for example.
As a result, Ra can be around 16 (i.e. 120 rpm at the crankshaft corresponding to 1920 rpm at the electric machine).
However, owing to the free wheel, the invention prevents the torque transmission from the engine to the electric machine at the end of the starting phase, and therefore prevents the engine from damaging the accessory pulley and/or pieces connected to it, such as a belt or the electric machine.
A significant advantage of the invention is that the use of a free wheel allows an automatic and immediate disconnection of the engine and the electric machine as soon as the combustion engine torque becomes positive. As a result, response time problems are avoided.
Subsequently, the drive system can be brought in another operating phase, typically in a running phase, in which the reduction ratio between the rotational speeds of the engine and the electric machine is different from Ra. In this operating phase, said ratio is Rb=R0×R1b, with R1b=1.
Moreover, the invention provides a drive system having a simple and robust construction, which moreover is fairly compact and has a fairly low weight.
The third junction element can further be configured to be coupled to the accessory pulley, in a second operating phase. The second operating phase can correspond to a running phase, in which the engine is running and drives the electric machine and the accessory.
In the second operating phase, the drive system is preferably configured such that the engine may receive power from the electric machine. In this case, the electric machine may use electric energy stored in the battery to boost the engine for performance or fuel consumption purpose.
The third junction element may be moveable between a first position, in the first operating phase, in which, in the mounted position, it is coupled to the free wheel, and another position, in an operating phase different from the first one, in which, in the mounted position, it is uncoupled from the free wheel.
More specifically, the third junction element may be moveable between a first position, in the first operating phase, in which, in the mounted position, it is coupled to the free wheel, and a second position, in the second operating phase, in which, in the mounted position, it is coupled to the accessory pulley. In an embodiment, the drive system has a main axis and the third junction element is moveable in translation along said main axis.
According to an embodiment, the third junction element comprises first coupling members for coupling with the free wheel, and second coupling members for coupling with the accessory pulley. For example, the first and/or second coupling members can comprise dog teeth.
The third junction element can further be configured to take a third position where it is uncoupled from the free wheel and from the accessory pulley, in a third operating phase. This third operating phase can correspond to an electric phase, in which the engine is stopped and the electric machine drives the accessory. When the third junction element is uncoupled from the free wheel and from the accessory pulley, it is in a third position that can be axially intermediate between the first and second positions.
In an embodiment, that the gear reduction mechanism can comprise an epicyclic gearing including a sun gear, an annular gear, planet gears meshing with both the sun gear and the annular gear and supported by a planet carrier.
Each of the sun gear, the annular gear and the planet carrier may be connected to one of the junction elements.
The first junction element can be connected to the planet carrier, preferably can be part of the planet carrier, the second junction element can be connected to the sun gear, preferably can be part of the sun gear, and the third junction element can be connected to the annular gear, preferably can be part of the annular gear.
Besides, in the mounted position, the free wheel may be fixedly mounted on a carter of the engine arrangement.
According to a second aspect, the invention relates to an engine arrangement comprising an engine, an electric machine, at least one accessory, and an accessory pulley to which the electric machine and the accessory are drivingly connected, and further comprising a drive system as previously described.
In practice, the at least one accessory can be one of: a water pump, an air conditioner compressor, a cooling fan.
The engine arrangement may further comprise at least one sensor for detecting the operating condition of the engine, a controller connected to said sensor and capable of controlling an actuator configured to allow coupling or uncoupling the third junction element of the gear reduction mechanism and the free wheel.
The actuator can be configured to move the third junction element of the gear reduction mechanism to place it in one of its first, second and third positions, depending on the detected engine operating condition. The operating condition of the engine can correspond to a current operating phase of the engine or to a desired operating phase of the engine, i.e. when the driver requires the engine to be started, stopped, or restarted.
According to a third aspect, the invention relates to a vehicle comprising an engine arrangement as previously described.
According to a fourth aspect, the invention relates to a method for operating an engine arrangement comprising an engine, an electric machine and at least one accessory, the electric machine and the accessory being drivingly connected to an accessory pulley, and a drive system comprising:
a gear reduction mechanism having at least three separate and rotatable junction elements, the rotation speeds of the junction elements being interdependent but not having a fixed ratio the ones relative to the others, the gear reduction mechanism joining the accessory pulley and an engine crankshaft via two junction elements of the gear reduction mechanism;
a free wheel which is connected to a non-rotating part of the engine arrangement and which can be coupled to the gear reduction mechanism via a third junction element of the gear reduction mechanism.
The method comprises the steps of:
a) detecting at least one parameter indicating if the engine is in a starting phase;
b) if the engine is in a starting phase, coupling the gear reduction mechanism to the free wheel;
c) in the starting phase, when the electric machine is starting the engine, operating the free wheel in an engaged state;
d) in the starting phase, when the engine has started and while the gear reduction mechanism is still coupled to the free wheel, operating the free wheel in a free state.
In other words, in step c), the gear reduction mechanism is coupled to the non-rotating part via the free wheel, and the system configuration is such that it allows transmission of torque from the electric machine to the engine. Subsequently, in step d), the gear reduction mechanism is uncoupled from the non-rotating part.
The use of the free wheel allows a very reactive control of the drive system and therefore improves the engine arrangement robustness and reliability.
In an embodiment:
step a) consists in or comprises detecting at least one parameter indicating if the engine is in a starting phase, a running phase or an electric phase, respectively; and
step b) consists in or comprises controlling the drive system to place the junction element of said gear reduction mechanism coupled to the free wheel if the engine is in a starting phase, coupled to the accessory pulley if the engine is in a running phase, or free from both the free wheel and the accessory pulley if the engine is in an electric phase.
In an embodiment, the drive system comprises an epicyclic gearing as the gear reduction mechanism, the epicyclic gearing including a sun gear, an annular gear, planet gears meshing with both the sun gear and the annular gear and supported by a planet carrier, the planet carrier being connected to the engine crankshaft and the sun gear being connected to the accessory pulley. Besides, step b) of the method consists in or comprises controlling the position of the annular gear relative to the free wheel or to the accessory pulley such that it can be coupled to the free wheel if the engine is in a starting phase, coupled to the accessory pulley if the engine is in a running phase, or uncoupled from both the free wheel and the accessory gear if the engine is in an electric phase.
The reduction ratio between the rotational speeds of the accessory pulley and the crankshaft can be:
R1b in the running phase, with R1b being substantially 1;
R1a in the starting phase, with R1a≠R1b, R1a being for example around 4.
Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims.